50 million-year-old testate amoebae

Testate amoebae have an extraordinarily long fossil record, with the oldest known fossils 750 to 700 million years old (Porter and Knoll, 2000; Bosak et al. 2011; Corsetti et al. 2003); however, knowledge of the evolutionary history of these single-celled organisms is surprisingly spotty.  In a recent paper in the journal Protist, Barber et al. help to fill this knowledge gap by describing some beautifully preserved testate amoeba remains from a ~50-million year old lake deposit.

A 163-meter long core was recovered from a kimberlite diatreme within the Slave Craton in the Northwest Territories of Canada in the Northwest Territories of Canada.

A 163-meter long core was recovered from a kimberlite diatreme within the Slave Craton in the Northwest Territories of Canada in the Northwest Territories of Canada.

Eocene-age scales probably representing testate amoebae in the genus Scutiglypha (from Barber et al. 2013).

Fossil scales above show the denticulate margin commonly found on plates bordering the aperture (from Barber et al. 2013).

The fossils represent plates of Euglyphid testate amoebae (Rhizaria: Euglyphida), a group of testate amoebae that construct siliceous shells, or tests, out of secreted plates. The plates are arranged on the shell in an overlapping fashion, and the morphology of individual plates varies by species and by location on the test. Barber et al. recovered several different types of plates in the deposit, and the remarkable preservation and abundance allowed even fine-scale features, like denticulate plate margins and pitting in the central portions of some plates, to be examined. Some of the fossil plates were morphologically indistinguishable from modern species of the genus Scutiglypha, suggesting that little evolutionary change in plate morphology has occurred for the last 50 million years, and perhaps much longer. Read the paper here.

Image of a modern specimen of Scutiglypha acanthophora showing the arrangement and morphology of plates on the test (from http://www.arcella.nl/).

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